Wettability Determination by Equilibrium Contact Angle Measurements Reservoir Rock - Connate Water System with Injection of CO2 (SPE 154382)

Carbon dioxide (CO2) injection into depleted gas reservoirs serves dual purposes: to enhance gas recovery and to store CO2. This process is largely controlled by the interactions among CO2, the reservoir fluid and rock. In particular, the wettability of the rock matrix has a strong effect on the distribution of CO2 injected in geological formation for sequestration. The rock wettability is determined by the three equilibrium interfacial tensions between the CO2, the connate water and the rock surface, which is one of the controlling parameters of the remaining fluid saturations, capillary pressure and relative permeability; hence conditioning the performance of any CO2 operation. In this study, the wetting behavior of CO2 on a Bentheimer sandstone surface in presence of synthetic connate water was investigated by means of visual contact-angle measurements. The experiments were conducted in a modified pendant drop cell at constant temperature of 318 K and pressures varying between 0.1- 16 MPa, typical in-situ conditions. This study shows that at a given temperature and pressure the dynamic contact angle increases over time to an equilibrium value. This equilibrium contact angle between the CO2/ water interface and the rock surface increases with pressure at constant temperature, indicating the rock surface becomes intermediate wet. In the range of pressure and salinity examined in this work, the system changes from strongly water-wet to intermediate wet. The system, however, does not become completely gas wet. Wetting behavior is very important for the design of an efficient CO2 storage process. Specifically, the alteration of the wettability of the rock in depleted gas reservoirs from strongly water-wet to intermediate or gas-wet changes the efficiency of the CO2 storage, because CO2 can imbibe into the rock matrix but also water banking might occur.